1. Field of the Invention
The present invention relates to a backlight device for generating light in, for example, a display for displaying a picture according to luminance based on the transmittance of the light, a lens used in the backlight device, a light source device, an electronic apparatus, and a light guide plate.
2. Description of Related Art
In recent years, as a backlight mounted in a liquid crystal display, backlights using LEDs (Light Emitting Diodes) as light source have been proposed and embodied into products. In a high-color-gamut LED backlight, LEDs independent for R (red), G (green) and B (blue) colors are used, whereby it has become possible to achieve color reproduction with an NTSC (National Television System Committee) ratio of 100% or more. Displays having such a LED backlight are now expected to be commercialized in the forms of PC (Personal Computer), amusement gears, or in-vehicle use.
In the case of backlights of intermediate sizes ranging from about 7 to 17 inches, it is essential to reduce the thickness of the backlight. Here, in the so-called directly underlying type backlight, LEDs are arranged on the rear side of the display surface of a liquid crystal panel and along the display surface. Most of large-sized backlights include the directly underlying type backlight. However, in order to realize a thin type backlight as above-mentioned, it is indispensable to design a backlight of the so-called edge light type (side edge type) in which light is emitted from an edge of a light guide plate. As an example of the edge light type backlight, a technology of backlight with a contrivance for keeping the luminescent surface uniform has been disclosed in Japanese Patent Laid-open No. Hei 11-212479 (hereinafter referred to as Patent Document 1).
The invention pertaining to backlight in Patent Document 1 aims not at a reduction in thickness but at eliminating irregularities in luminance and contriving a reduced weight, even in a large-sized display (refer to, for example, paragraphs [0016], [0017], etc., FIGS. 1 and 3 of Patent Document 1). Specifically, as shown in FIG. 1 in Patent Document 1, four light sources (3) are provided so as to secure a predetermined luminance, and a clearance (11) is provided between light guide plates (9), (10) so as to contrive a reduced weight. In addition, as shown in FIG. 3 of Patent Document 1, cylindrical lenses (12) is disposed along both end parts of the clearance (11), whereby the light emitted from the light sources (3) is converged, and is uniformly dispersed in the area ranging from end parts to central parts of the light guide plates (9), (10). Incidentally, the light sources (3) are composed of hot cathode tubes or cold cathode tubes, as described in paragraph [0002] of the specification of Patent Document 1.
As a backlight using LEDs as light sources, a backlight reduced in luminance irregularities has been proposed (refer to, for example, Japanese Patent Laid-open No. 2005-196989 (hereinafter referred to as Patent Document 2)). In this backlight, the luminous intensity distributions of the RGB LEDs are controlled to within predetermined ranges, whereby irregularities in color and in luminance are reduced (refer to, for example, paragraph [0058], FIG. 3 of Patent Document 2).